How to Measure a Bicycle Thru-Axle

Over Locknut Dimension

Four different measurements are most commonly used for thru-axles. They usually are written something like this: 12mm x 142mm, L163 length, TP 1.5

In this example, 12mm is the diameter, 142mm is the O.L.D. (Over Locknut Dimension), 163mm is the overall length and 1.5mm is the thread pitch. You can see these measurements in more detail below:

12mm and 15mm are the most common axle diameters. It’s best to measure with a caliper in millimeters, but you should also be able to figure it out with a ruler in most cases.



We find that the O.L.D. is frequently confused with the overall length and this often causes people to order the wrong size axle. The best way to find the right size you need is to measure the original axle you are replacing. The overall length is measured from the base of the head (underneath it) to the end of the threads.
If you can’t measure your existing thru-axle, try checking with the manufacturer to see if they list the specifications (Ask them for the 4 measurements listed above). Some people try to guess by measuring the outside-to-outside measurement. Although this isn’t ideal, it sometimes can give you an idea of what you need as this measurement is usually about 20 to 30mm more than the O.L.D. The thru-axle needs to be long enough to go through the thickness of the frame or fork. You also don’t want the axle to be too short and/or narrow or the threading may not hold securely.

Thread Pitch and Thread Length

The thread pitch (TP) for a thru-axle is the distance from the ridge of one thread to the ridge of the next thread and is also measured in millimeters. A 1.5 mm thread pitch is finer than a 1.75 mm pitch but coarser than a 1 mm pitch. This measurement can be hard to determine without a caliper. Try to find the manufacturer specs for your fork or frame if you’re unsure of your measurements.
All our thru-axles will also list the length of the threaded section.

The Distance In-Between Your Fork or Frame

As we have mentioned before, this is also known as O.L.D. or Over Locknut Dimension. For a front thru-axle, this is measured from the inside to the inside of your fork. For a rear thru-axle, this is measured from the inside to the inside of your frame at the drop-outs. The O.L.D. measurement is often listed for many thru-axles but isn’t necessary if you know the overall length. We also have found that most websites list the O.L.D. in the specs but do not always list the overall axle length. This also causes confusion and often leads to incorrect orders from our customers.

Common Sizes for Frames:
130mm, 135mm, 142mm, 148mm, 197mm. 148mm is often referred to as Boost Sizing, 157mm- super boost. 197mm is sometimes called Fat.

Common Sizes for Forks:
100mm, 110mm and 150mm are common fork sizes.

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